Liquid coating composition



Patented July 25, 1939 PATENT OFF-ICE LIQUID COATING COMPOSITION Carlos Tobis, Berlin-Oberschoneweide, Germany,

assignor to General Electric Company, a corporation of New York- No Drawing. Application August 19, 1937, Serial No. 159,973. In Germany October 24, 1938 2 claim." (01. 260-32) The present invention relates broadly to a liquid coating composition and more particularly to liquid coating compositions of the kind known to the trade as "wire enamels". The invention is especially directed toa newand useful composition comprising a combination of particular polymerized acrylic acid derivatives and a particular organic solvent mixture for said derivatives.

In the manufacture of insulated electrical conductors so-called organic enamels" heretofore have been widely used. Such enamels have been made of varying compositions, but to a large extent have depended on the use of various drying oils, such as linseed oil, China-wood oil, and the like, as essential components. The need for more satisfactory insulation for metallic conductors, such as copper in wire or other form, has resulted in increased attention to synthetic materials as electrical insulation. Recently, too, there has been increased demand for electrically insulating compositions which maintain their stability in the presence of various impregnants and filling substances such as waxes, oils, oilresin mixtures, etc., which are used in the manufacture of certain types of electrical apparatus.

In the co-pending application of Paul Nowak, Hermann Hofmeier and Carlos 'lobis, Serial No. 159,972, filed Aug. 19, 1937, and assigned to the same assignee as the present invention, there was disclosed and claimed an insulated electrical conductor having as insulation a combination of particular polymerized acrylic acid derivatives heated to the point of dissociation thereof. The present invention is directed to a liquid coating composition or baking enamel adapted for use in carrying into effect the invention disclosed and claimed in the aforesaid co-pending application.

As pointed out in the above-identified copending application mixed polymerizates of esters of acrylic acid and acrylic acid nitrile (acrylonitrile) have been found to be particularly advantageous for' use as insulation for electrical conductors. These substances show the required stability against solvents of all kinds to which the insulated conductor may be exposed during processes of manufacturing electrical apparatus utilizing such conductor or during subsequent service use of the same.

As a result of the high resistance to solvents of a synthetic composition consisting of polymerized acrylic acid ester (or esters) and polymerized acrylic acid nitrile, due particularly to the polymerized acrylic acid nitrile component, the selection of a suitable solvent or mixture of solvents for making a liquid coating composition from such mixed polymerizates causes considerable difliculties. In the case of conventional oil varnishes this problem is not encountered, since such varnishes readily may be dissolved in known solvents, for example, benzene, petroleum naphthas and the like.

Furthermore, when applying a varnish containing a mixed polymerizate of acrylic acid ester and acrylic acid nitrile to a wire by means of conventional wire-enameling apparatus, it has been found that unsatisfactory results are obtained when the said varnish base is dissolved in a single chemical substance and which, therefore, possesses a definite boiling point. It has been found that .a suitable insulating coating is obtained only when a. solvent is used that boils over a longer range than do the conventional varnish solvents.

More specifically it may be stated that, in accordance with the present invention, there is used as solvent for the aforementioned mixed polymerizates a mixture comprising diethylene dioxide (dioxan), monochlorbenzene, 'cyclohexanone, dichlordiethyl ether and ethylene glycol diacetate. By using these components, mixtures can be prepared with boiling points that, by varying the proportions of the individual components, may be made closely to approximate the boiling points of the conventional solvents or solvent mixtures employed in the manufacture of the usual oil varnishes. One such solvent has, for example, the following composition:

Per cent by weight Diethylene dioxide (dioxan) 25 Monochlorbenzene 30 Cyclohexanone 30 Dichlordiethyl ether 10 Ethylene glycol diacetate 5 These percentage proportions are not limited thereto but may be varied with variations, for example, in the selected polymerized acrylic acid ester or mixture of esters andwlth variations in the ratio of the polymerized acrylic acid nitrile component of the varnish to such ester or esters.

In addition to the aforedescribed organic solvent component, liquid coating compositions prdduced in accordance with the present invention contain a synthetic composition consisting of a polymerized ester of acrylic acid, for example, polymerized acrylic acid methyl ester, ethyl ester, butyl ester, etc., or mixtures of such esters, and, in addition thereto, polymerized acrylic acid nitrile, When polymerized acrylic acid nitrile is present in a varnish which also contains a polymerized ester acrylic acid, the composition may be heated to the point of dissociation oi the basic materials without lowering the insulating properties of the dried coating as a result of the presence therein of objectionable dissociation products. l

Both mixtures of polymerized acrylic acid esters and polymerized acrylic acid nitrile and also mixed polymerizates resulting from the conjoint polymerization of monomeric acrylic acid esters and acrylic acid nitrile may be used in preparing varnishes of the present invention. varnishes may be made from the mixed monomeric acrylic acid ester (or esters) and acrylic acid nitrile and subsequently may be partially or completely polymerized while in solutionin the specified solvent. By a suitable selection of the ratio of acrylic acid ester to acrylic acid nitrile, and by controlling the degree of polymerization, it is possible to adapt the varnish films to the requirements of a particular service use, at least in so far as their mechanical and chemical properties are concerned. In this manner the hardness, elasticity and softening point of the dried film may be varied within wide limits. The percentage of acrylic acid nitrile is predetermined, and may be varied within wide limits depending upon the properties desired in the dried coating. It is preferable to use at least about per cent by weight of acrylic acid nitrile, the remainder of the basic material of the composition consisting essentially of acrylic acid ester (or esters). Ordinarily, varnish made in accordance with the present invention will contain not more than about 65 per cent by weight of acrylic acid nitrile mixed with about 35 per cent by weight of acrylic acid ester or mixture of esters. The ratios mentioned refer to the components in monomeric, or in partially or completely polymerized state, that is, in whatever their particular state may be when made into a varnish composition. Compostions produced in accordance with the present invention may be heated (baked) to remove solvent without the formation of objectionable dissociation products, even when the material is heated or baked to such an extent that the dried varnish film is almost black.

Dried or baked films resulting from heating liquid coating compositions or baking enamels oi the present invention to evaporate solvent therefrom difier in their external appearance in no way from conventional oil varnish films, but possess the previously mentioned advantages of increased resistance to solvents. The dried films also show improved mechanical and electrical giglperties as compared with ordinary oil varnish s. What I claim as new and desire to secure by Letters Patent of the United States is:

1. A baking enamel comprising a mixture of polymerized ester of acrylic acid and polymerized acrylonitrile and an organic solvent for said mixture comprising a mixture of diethylene dioxide, monochlorbenzene, oyclohexanone, dichlordiethyl ether and ethylene glycol diacetate.

2. A baking enamel comprising a synthetic composition consisting, by weight, of at least 10 per cent and not in excess substantially of 65 per cent polymerized acrylonitrile and the remainder polymerized ethyl ester of acrylic acid, and as a solvent for said synthetic composition a mixture having the following approximate composition:

Parts by weight Diethylene dioxide 25 Monochlorbenzene 30 Cyclohexanone 30 Dichlordiethyl ether 10 Ethylene glycol diacetate 5 CARLOS T0318. 

